Method for dying a web of knitted fabric containing cellulose fibers

ABSTRACT

A method for dyeing a web of knitted fabric containing cellulose fibers is described. In order to achieve the result of being able to continuously dye the knitted goods containing cellulose fibers in the spread-out state, using a pad, as well as dry it in-line, in a subsequent dyeing hotflue, and fix the color, the knitted fabric is first caught along the longitudinal edges in continuously transporting stentering chains, and then transverse strips of glue are applied to the longitudinal edges, reinforcing the longitudinal edge regions, adjacent to the stentering chains. The glue is dried and subsequently the web that has been released from the stentering chains is passed continuously through the dyeing pad and the dyeing hotflue, spread out, fundamentally like a woven web of fabric.

The invention relates to a method for dyeing a web of knitted fabriccontaining cellulose fibers, whereby strips of glue are applied to theedge regions, adjacent to the longitudinal edges of the fabric web,before dyeing, and stiffened by means of drying, whereby the fabric webis dyed in a dyeing pad and then dried in a dyeing hotflue and the coloris fixed.

Knitted fabric is generally produced as a tube. The fabric web is formedin that the tube is cut open parallel to its longitudinal axis, on asstraight a line as possible. The cut edges that are formed in thisconnection tend to curl up. “Containing cellulose fibers” means that theknitted fabric consists entirely or in part of cellulose fibers.

When dyeing webs of woven fabric, the edges of which normally do notcurl up on their own, continuous dyeing according to the so-calledpad-dry principle is usual. Here, the fabric web is passed through adyeing pad. Subsequently, in other words in line, continuously, the dyedfabric web is dried in a dyeing hotflue and the color is fixed. In ahotflue, the fabric web has no hold on the sides. Therefore,conventionally the pad-dry method can only be used for woven andsimilarly area-stable fabric webs.

Fabric webs consisting of knitted fabrics that contain cellulose fibersare, in contrast, treated according to the so-called drawing method, oraccording to the cold-pad batch principle, if dyeing is required. Thesemethods operate discontinuously. They are therefore complicated andtime-consuming.

Methods for continuous dyeing of knitted fabrics are known from DE 10135 044 A1 and DE 101 31 000 A1, whereby either the entire area is(temporarily) stiffened, or so-called ancillary edges are applied ontothe in the edge region and later removed again. In these references, itis stated that the goods must be stiffened “before” the dyeing process(over the entire area or at the edges). This pretreatment is thereforenot carried out continuously, in one pass with the dyeing.

DE 32 38 378 A1 discloses various forms of edge glue strips and/orstiffening zones at the edge of a web of knitted fabric that tends tocurl up. DE 195 22 124 A1 describes edge gluing on a stentering frame.In this connection, the information that the hot-melt glue is applied tothe edges of the knitted fabric at the outlet of the stentering frameshould be noted.

The invention is based on the task of creating a dyeing system forcontinuous dyeing of knitted fabric, which replaces the time-consumingmethods according to the drawing method or according to the cold-padbatch principle, which have been usual up to now, in dyeing cellulosefibers. The primary concern is to continuously treat a web of knittedfabric that contains cellulose fibers, in one pass, from spreading thefabric web out to drying it and fixing the color.

The solution according to the invention is indicated in claim 1. It ispreferably characterized, for the method stated initially, by acontinuous run of the fabric web, with the following stages, i.e. steps:

-   -   a) Spreading out the fabric web, which tends to curl up at both        longitudinal web edges;    -   b) Continuously stentering the fabric web, by means of attaching        the two longitudinal edges to continuously transporting        stentering chains;    -   c) Applying the glue strips in the form of transverse glue        strips, whereby the width of the glue strip (measured proceeding        from the edge of the fabric web crosswise to the running        direction) is on the order of 1/25 of the axial distance between        the upper and lower roller basket of the dyeing hotflue, but at        least approximately 1 cm;    -   d) Releasing the fabric web from the stentering chains before it        runs into the dyeing pad; and    -   e) Using a dyeing hotflue that is designed to guide the fabric        web with a particularly uniform and extremely low longitudinal        tension of the fabric, namely on the order of 10 newtons, with a        maximal variation range of 5 newtons.

Preferably, a delivery of the dyed and dried fabric web that is free oflongitudinal and transverse tension can follow. Some improvements andfurther embodiments of the invention are described in the dependentclaims.

The state of the art described above, referring to DE 101 35 044 A1 andDE 101 31 000 A1, does disclose the stiffening of at least the edgeregions of a web of knitted fabric, and the dyeing, drying, and colorfixation of the dyed fabric web, which take place discontinuously, in ahotflue. However, the state of the art does not give any indications asto how stiffening of the edge zones is supposed to be continuouslycarried out ahead of the dyeing, drying, and color-fixing process. Butthis precisely is the concern of the present invention. It cannot havebeen made obvious by the state of the art, as a whole, because accordingto the knowledge of a person skilled in the art, introduction of thefabric web having edges that tend to curl up into a continuous workprocess presupposes an edge stiffening (that has already been produced).

In other words: In order to achieve the result that a web of knittedfabric that contains cellulose fibers can be continuously dyed, in thespread-out state, using a pad, as well as dried in-line in a subsequentdyeing hotflue, and the color can be fixed, the knitted fabric is firstcaught along the longitudinal edges in continuously transportingstentering chains, and then glue that reinforces the longitudinal edgeregions is applied to the longitudinal edges held in the stenteringchains, adjacent to them, and subsequently (despite having been releasedfrom the stentering chains) the web is continuously, in other wordsin-line, passed through the dyeing pad and the dyeing hotflue, spreadout, fundamentally like a woven web of fabric. Preferably, the upperand/or lower rollers of the hotflue should be driven.

In a hotflue used for color fixation and drying, for example accordingto DE 33 36 328 C2, the fabric web is passed up and down over guiderollers, in a meander shape, with a certain longitudinal tension. In thehotflue, there is a series of guide rollers that lie essentiallyparallel to one another, in the lower region and in the upper region, ineach instance (so-called upper and lower rollers), approximately in acommon plane, in each instance. Generally, heated air is blown into theloops of fabric web that are stretched between two upper or between twolower guide rollers, in each instance, from above or from below,respectively for drying and fixing.

Without a certain longitudinal tension, a fabric web cannot be movedthrough such a hotflue. In the case of webs of woven fabric, thisgenerally does not cause a problem, but in the case of webs of knittedfabric (not having edge regions stabilized according to the invention)the longitudinal tension has the result that the fabric web does notremain spread out in the machine (as it runs over the guide rollers) butinstead, the edges curl up more and more as it passes through theindividual loops of the hotflue, and in an extreme case, the spread-outweb turns into a skein. In the case of such a skein, the advantages ofthe hotflue do not have their effect, so that knitted fabricconventionally cannot be dried in a hotflue, and the color cannot befixed.

According to the invention, it is proposed to stiffen merely the edgeregions, which are narrow relative to the overall width of the fabricweb, using transverse glue strips or similar stabilization means.Surprisingly, this stiffening of the narrow edge regions alone has theresult that the web of knitted fabric does not run together into a skeinin the hotflue, but instead passes through the hotflue spread out like aweb of woven fabric. It is advantageous in this connection that the gluetracks at the two fabric web edges are not continuous but interrupted.For example, approximately two length units of a glue-free region aresupposed to follow one length unit of a glued transverse strip (seen inthe running direction of the fabric web). In practice, such a ratio onthe order of 1:2 has proven itself.

The width of the glue track (measured transverse to the runningdirection, starting at the edge of the fabric web) depends, according tothe invention, on the distance between the upper and the lower rollersof the dyeing hotflue. The greater the distance, the wider the gluestrip has to be made, in order to exclude curling up or folding over ofthe stiffened edges on their path between two rollers, in each instance.It has turned out that this edge curl-up can be prevented if the widthof the glue strips (that is the length of the glue strips), proceedingfrom the edge of the fabric web, is greater than approximately 1/25 ofthe axial distance between the upper and lower hotflue roller, accordingto the invention. The width of the glue strip should be at leastapproximately 1 cm.

The lower the longitudinal tensile force that acts on the fabric web,the easier it is to prevent turn-over or curl-up of the edges. Likewise,it is advantageous, within the scope of the invention, if thelongitudinal tensile force that acts on the fabric web is approximatelyuniform everywhere in the hotflue, in other words in every fabric loop.In order to achieve this uniform, low longitudinal fabric tensionthroughout the entire dyeing hotflue, it is advantageous to drive theupper rollers not jointly by way of a chain drive, but rather to driveeach individual upper roller, but at most two or three rollers together,in each instance (depending on the weight of the fabric), with aseparate motor that has an adjustable drive moment.

Within the scope of the invention, the information “drying andcolor-fixing” means not only color-fixing during drying, but also dryingand subsequent color-fixing. Once the fabric web has been dried andfixed, it can be delivered to a roll, or to a stack, by way of alay-down device, without longitudinal or transverse tension, as is usualfor woven fabric. Alternatively, the fabric web can first be treated inthe hotflue, essentially for the purpose of fixation, and then be washedand dried in-line, with continuous further processing, as well asdelivered essentially free of longitudinal and transverse tension.

Details of the invention will be explained using the attachedrepresentation of an exemplary embodiment of the system conceptaccording to the invention, for continuous dyeing of a spread-out web ofknitted fabric that consists at least in part of cellulose fibers. Thefigures show:

FIG. 1 a system in schematic, vertical cross-section; and

FIG. 2 a top view of a part of the system according to FIG. 1.

The fabric web 1 runs in the transport direction 2 (longitudinaldirection of the fabric web) from the roller 3 through a spreadingdevice 4 into a type of stentering frame 5, which is also shown in FIG.2, in the top view, in principle. The stentering frame 5 possesses twostentering chains 6 and 7, which are equipped with needles 8(alternatively, tenterhooks are also possible) for needling the edgeregions 9 onto the longitudinal edges 10 of the fabric web 1. Each ofthe stentering chains runs, in endless manner, over chain wheels 11(having a horizontal or vertical wheel axle 12). When the fabric web 1,i.e. its edge regions 9 are fixed in the chain 6, 7, in each instance,transverse glue strips are applied to the edge regions 9 in a gluingstation 13. The length b of the transverse glue strips (seen crosswiseto the transport direction 2) is supposed to be small relative to thetotal width B of the fabric web 1, and made to be approximately equal to1/25 of the distance between the upper and lower rollers of the hotfluedescribed below. The glue applied is stiffened in an edge drying station14 that follows in the transport direction 2. As a result, the edgeregions 9 lose their flexibility, which is typical for knitted fabric,so that the edges no longer curl up after the textile web 1 has beenreleased at the exit 15 of the stentering frame 5.

The fabric web 1 is subsequently brought into a dyeing pad 17 having animmersion roller 18 and subsequent pair 19 of squeezing rollers, by wayof a guide roller 16, to the inlet slit 20 of a dyeing hotfluedesignated as a whole as 21. In the hotflue 21, the fabric web 1 runsover a deflection roller 22 as well as in meander shape downward andupward over two series 23 and 24 of guide rollers, each of whichconsists of a plurality of guide rollers, namely lower rollers 25 andupper rollers 26. Within the hotflue 21, heated air is applied to theloops 27 of fabric web stretched between two guide rollers 25, 26 or aroller series 23, 24, in each instance, from blowing nozzles 28. At theend of the fabric web run in the hotflue 21, the fabric web 1 reaches arun-out region 31, e.g. having a support strip 32, by way of adeflection roller 29 and an outlet slit 30, for delivery of the fabricweb 1 onto a roller 33, free of longitudinal and transverse tension.

REFERENCE SYMBOL LIST

-   1=fabric web-   2=transport direction-   3=roller-   4=spreading device-   5=stentering frame-   6, 7=stentering chains-   8=needles-   9=edge region-   10=longitudinal edges-   11=chain wheel-   12=wheel axle-   13=gluing station-   14=drying station-   15=exit (5)-   16=guide roller-   17=dyeing pad-   18=immersion roller-   19=squeegee-   20=inlet slit-   21=dyeing hotflue-   22=deflection wheel-   23, 24=series of guide rollers-   25=lower roller-   26=upper roller-   27=fabric web loop-   28=blowing nozzle-   29=deflection roller-   30=outlet slit-   31=run-out region-   32=support strip-   33=roller

1. Method for dyeing a web of knitted fabric (1) containing cellulosefibers, whereby strips of glue are applied to the edge regions (9),adjacent to the longitudinal edges (10) of the fabric web, beforedyeing, and stiffened by means of drying, whereby the fabric web is dyedin a dyeing pad (17) and then dried in a dyeing hotflue (21) and thecolor is fixed, comprising the following stages, i.e. steps: a)Spreading out the fabric web (1), which tends to curl up at bothlongitudinal web edges (10); b) Continuously stentering the fabric web(1), by means of attaching the two longitudinal edges (10) tocontinuously transporting stentering chains (6, 7); c) Applying gluestrips in the fabric web running direction (2), in the form oftransverse glue strips interrupted by glue-free regions, whereby thelength of the glue strips (measured proceeding from the edge of thefabric web crosswise to the running direction) is on the order of 1/25of the axial distance between the upper and lower rollers (25, 26) ofthe dyeing hotflue (21), but at least approximately 1 cm; d) Releasingthe fabric web (1) from the stentering chains (6, 7) before it runs intothe dyeing pad (17); and e) Designing the dyeing hotflue (21) to guidethe fabric web (1) with a uniform longitudinal tension of the fabric onthe order of 10 newtons±5 newtons.
 2. Method according to claim 1,wherein a dyeing hotflue (21) having lower and/or upper rollers (24, 25)that are driven individually or in groups is used.
 3. Method accordingto claim 1, wherein the transverse glue strips, seen in the web runningdirection (2), are made to be on the order of twice as wide as theregions free of glue.